For the manufacture of molds for the manufacture of shaped plastic articles, plastic mold steel 40 CrMnMo 7, work material no. 1.2311 or the variant alloyed with sulfur, 40 CrMnMoS 86, work material no. 1.2312 are primarily used. These steels are quenched and tempered by the manufacturer to tensile strength values of 900 to 1100 N/mm.sup.2 and processed in this state into molds or tools. A subsequent heat treatment of the tools would result in unacceptable dimensional changes, distortions or surface impairments. As a consequence, the quenching and tempering strength remains limited at 1100 to 1200 N/mm.sup.2 because higher strengths would make it more difficult to machine the steel.
The traditional martensite steels with 18% nickel, 8% cobalt, 5% molybdenum and up to 1.4% titanium, which exhibit a tensile strength of approximately 1000 N/mm.sup.2 in the solution heat treatment state and which can be aged to strengths above 2000 N/mm.sup.2, are considered for the production of plastic molds only to a limited extent, because of their high alloy content and the associated expenses.